In the last four months, China has forged an aggressive, more nationalistic posture in Asia that may set the tone for Mr. Xi’s expected decade-long tenure, analysts and diplomats say, pushing against American allies, particularly Japan, for what China considers its territorial imperatives. The son of a revolutionary general, Mr. Xi, 59, boasts far closer ties to China’s fast-growing military than the departing leader, Hu Jintao, had when he took office. As Mr. Xi rose through the ranks of the Communist Party, he made the most of parallel posts in the People’s Liberation Army, deeply familiarizing himself with the inner workings of the armed forces.

Even if Mr. Xi does not immediately become head of the crucial Central Military Commission as well as party leader, he will almost certainly do so within two years, giving him at least eight years as the direct overseer of the military.

This combination of political power as head of the Communist Party and good relations with a more robust military could make Mr. Xi a formidable leader for Washington to contend with, analysts and diplomats in China and the United States say.

“The basic question is whether Xi will suspend the drift in the U.S.-China relationship and take concrete steps to put it on a more positive footing — or will he put it on a different, more confrontational track?” said Christopher K. Johnson, senior adviser at the Center for Strategic and International Studies in Washington, and until recently a China analyst at the Central Intelligence Agency.

“We talked to a number of people in Hangzhou and other towns when he was in charge” of Zhejiang, Rittenberg said. “They really seemed to love this guy. He was approachable and had a democratic style. He listens to people. He keeps his ear to the ground and never made life hard for political opponents.”

At the same time, Xi’s time as vice president shows that he adheres to core Communist Party rhetoric, such as the lectures at the central party school in Beijing, which he heads, discussing the theories of Karl Marx and Vladimir Lenin.

“Now Hu Jintao’s era (is the) past, now Xi Jinping is coming as president. I think there’s no alternative except some political change, so political reform. Economy reform (is) already there” the Dalai Lama told reporters while on a pastoral visit to Japan.

He acknowledged that economic reforms had produced benefits for China, but said the resort to force by the authorities was at odds with their aim of creating a “harmonious society”.